Method for setting up virtual connections in switching equipment operating according to an asynchronous transfer mode

ABSTRACT

For route searching in a multi-stage ATM switching matrix network, the free transmission capacities of ATM links are individually stored with an occupation memory. For setting up new virtual connections, a required transmission capacity is reported. Based on the extent thereof, a route selection occurs only via ATM links having free transmission capacity that is momentarily adequate. Bit rate classes are formed for storing the free transmission capacity. The required transmission capacities are also classified therein. For a respective ATM link group that is connected to an ATM switching element at the output side and/or input side, link-associated storage locations are binarily identified in storage cells of the occupation memory provided per bit rate class when transmission capacity corresponding to the allocated bit rate class is still respectively freely available. Presence of coincidence in view of the binary identification established for the respective bit rate class is checked in the route searching.

BACKGROUND OF THE INVENTION

The invention is directed to a method for setting up virtual connectionsin switching equipment operating according to an asynchronous transfermode.

Methods of this type are already known from the periodical INTERNATIONALJOURNAL OF DIGITAL AND ANALOG CABLED SYSTEMS, Vol. 1, an article by K.A. Lutz on pages 237-243 (1988) and from the Conference Paper from theInternational Switching Symposium, 15 through Mar. 20, 1987,Proceedings, Phoenix, USA, Bouch, K. Bruninghaus, and B. Schaffer3(1987), pages 602-608, both incorporated herein by reference. Virtualconnections are set up for packet switching with methods of the knowntype. For this purpose, routes sought via links as well as via ATM(Asynchronous Transfer Mode)--switching matrix networks, are selectedand defined. Routes via ATM switching elements and via ATM links aredefined within an ATM switching matrix network.

It is important when seeking, selecting, and defining routes (routesearch) for virtual connections to be newly set up that routes alreadyoccupied by virtual connections can be made use of for other virtualconnections, insofar as free transmission capacity is still available onthese routes. For this purpose, it is known--for example for every linkin a multi-stage ATM switching matrix network--to store the transmissioncapacity that is respectively free at the moment, i.e. is available forsetting up new virtual connections, in an ATM link occupation memory.This transmission capacity that is still free, i.e. is stillrespectively available for setting up new virtual connections, can, forexample, be equal to the difference between the overall transmissioncapacity of a link and the transmission capacity already made use of bythe virtual connections set up thereover. The latter, for example, canbe the sum of all peak bit rates of the corresponding virtualconnections.

It is already known for seeking, selecting, and defining routes forvirtual connections to be newly set up that the respective transmissioncapacity that is still free, i.e. is still available for setting up newvirtual connections, is compared in terms of size to the transmissioncapacity required for the new virtual connection to be set up, which,for example, may correspond to the peak bit rate of this virtualconnection.

The invention is directed to simplifying the procedure of routesearching to be very frequently sequenced in methods of the typeinitially discussed. When a size comparison of the type addressed aboveis then carried out for every route search, then particularly strictdemands for the corresponding processing equipment result therefrom,namely because the operations of setting up new virtual connections, onthe one hand, are many per time unit, i.e. occur relatively frequentlyand, on the other hand, dare not last too long. Waiting time problemswhen setting up connections are disturbing and undesirable.

SUMMARY OF THE INVENTION

It is an object of the invention to specify suitable techniques for amethod of the type initially cited with the assistance of which theseeking, selection, and definition of routes (route search) for virtualconnections to be newly set up can be sequenced as simply as possible.The processing events should be designed such that all events that areto be sequenced immediately before every new virtual connection and forevery piece of equipment are optimally simplified.

According to the invention, a method is provided for setting up virtualconnections in ATM switching equipment operating according to anasynchronous transfer mode. A multi-stage ATM switching matrix networkis provided having a plurality of switching matrix stages each having aplurality of ATM switching elements. ATM links lead from switchingmatrix stage to switching matrix stage. The ATM switching elementsconnect successive switching matrix stages to one another. Bit ratelimit values are defined in call-associated fashion for individualvirtual connections by storing appropriate data. An ATM link occupationmemory is provided for set-up of new virtual connections by selectingcall-associated roots, free bit rate transmission capacities which arestill available being individually stored for the ATM links.Acceptability of the set-up of new virtual connections with respect toeach and every one of the ATM links coming into consideration for theseconnections is checked by use of the bit rate limit values defined forthe new virtual connections and by use of the free bit rate transmissioncapacity that is still respectively available on the corresponding ATMlinks. The virtual connections are allocated to connection bit rateclasses referring to dimensional ranges of the bit rate limit values.The free bit rate transmission capacities still respectively availableon the ATM links are allocated to transmission bit rate classes havingcorresponding transmission bit rate limit values. ATM links respectivelyexiting from one of the ATM switching elements and/or leading to such anATM switching element are combined into an ATM link group. A family ofstorage cells each having a respective plurality of storage locations isreserved in the ATM link occupation memory for each of the ATM linkgroups. Each of the storage cells is allocated to a defined connectionbit rate class or transmission bit rate class, and within the respectivestorage cell, each of the storage locations is allocated to one of theATM links connected to the respective ATM switching element. Theindividual storage locations of a storage cell are marked in binaryfashion given a presence of a free transmission capacity on theallocated ATM link for the transmission bit rate class allocated to therespective storage cell. For setting up a new virtual connection via aplurality of ATM links corresponding in number to the plurality ofswitching matrix stages, a storage cell corresponding to the connectionbit rate class allocated to the new virtual connection is selected forevery one of the ATM link groups coming into consideration. On the basisof an interrogation event of the individual storage locationsidentically identified with respect to the sequence within the storagecells just being driven, those ATM links whose allocated storagelocations have a coincidency with respect to their binary identificationare selected for the new virtual connection.

As a result of the invention, the size comparisons between availabletransmission capacities and required transmission capacities are reducedto simple one-bit comparisons. The route search for virtual connectionsto be newly set up is thus quite significantly simplified, this being ofparticular significance for virtual connections via ATM switching matrixnetworks having a plurality of switching matrix stages and, accordingly,via various groups of ATM links. These groups lie at different locationsbetween the successive switching matrix stages in the ATM switchingmatrix network. Connection bit rate classes are then formed for thispurpose. Respectively proceeding from the connection bit rate classapplying to the virtual connection to be newly set up, a route searchmakes use of the various memory elements corresponding to thisconnection bit rate class, and on the basis of simple one-bitcomparisons, identifies the ATM links that are respectively usable forthe new virtual connection to be set up.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing shows an ATM switching equipment system operating in anasynchronous transfer mode, and which operates according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As an exemplary embodiment, the drawing shows switching equipmentwherein the invention is employed. Only those component parts servingfor an understanding of the instant invention are thus shown for thisswitching equipment.

An ATM switching matrix network K (referred to below as a "switchingmatrix network" for purposes of simplification) of ATM switchingequipment contains ATM switching elements v11 through v3n (referred tobelow only as "switching element" or, respectively, "switchingelements") in three switching matrix stages K1 through K3. Theseswitching elements are connected to one another via links Z111 throughZm3n in the illustrated way. ATM switching equipment in communicationequipment having the asynchronous transfer mode (ATM) is already knownfrom extensive technical literature, a few exemplary examples thereofbeing referenced: "International Zuerich Seminar on DigitalCommunications", (March 1986) with the publication "New Directions inCommunications" (Section A3.1 through A3.8 by J. B. Turner); GermanPublished Application 3 732 937; European Patent Application 89102172.7;Periodical "Nachrichtentechnik, Elektronik," Berlin, 39 (1989)1, pages 3and 4, all incorporated herein by reference.

The switching equipment shown in the drawing is thus a switchingarrangement for communication equipment having the asynchronous transfermode. Virtual connections are set up via the multi-stage switchingmatrix network K. For this purpose, ATM links z111 through zm3n leadfrom switching matrix stage to switching matrix stage. They connect theswitching matrices v11 through v3n of the three successive switchingmatrix stages K1 through K3 to one another. For virtual connectionsthat, as is known, serve the purpose of packet-switched transmission ofdata and messages, call-associated routes are sought, selected, anddefined. By contrast to PCM connections and conventionally voltaicallythrough-connected connections, as is known these virtual connections arenot provided in such fashion that a connecting path (this can thus be apath that is voltaically through-connected or through-connected intime-division multiplex) can be exclusively used for only oneconnection; rather, virtual connections are of such a nature thatinformation in the form of message packets (cells) are communicated withthem, that these packets (cells) are identified with a header, and thatall packets (cells) of a virtual connection respectively follow the sameroute across the switching matrix network and links in the network thatwas selected during set-up. Message packets or data packets to becommunicated via virtual connections are communicated packet-by-packet.Accordingly, further data packets, namely different virtual connections,are communicated chronologically between the data packets to becommunicated for the corresponding virtual connection being communicatedvia the corresponding connecting paths, for example transmissionchannels of transmission systems and links. As is known, however,virtual connections are exactly defined in terms of route. Correspondingroute searching and selection means serve this purpose in thecorresponding switching centers.

What, among other things, is thus involved when setting up virtualconnections via ATM switching equipment is that only so many virtualconnections can be conducted via corresponding ATM connecting paths (forexample ATM links), in view of the given transmission capacity. For thispurpose, call-associated bit rate limit values for virtual connectionsin ATM switching equipment are defined by storing appropriate data.These bit rate limit values, for example, can be the peak bit rates ofthe corresponding virtual connections. When a subscriber wishes theset-up of a new virtual connection, then he indicates the peak bit ratewith which he intends to transmit (messages, data, and the like). Duringtransmission of data packets, he fundamentally dares not exceed thispeak bit rate. In a first ATM switching center in which data packetstransmitted by the corresponding subscriber arrive, constant monitoringis carried out to see whether the incoming ATM message stream observesor exceeds the rate values announced by the corresponding subscriber inview of the peak bit rate; corresponding counter-measures are initiatedin the switching center given an upward transgression. This can becomprised therein that parts of the message packets are suppressed, i.e.are not transmitted at all or are transmitted in truncated fashion;and/or in that a corresponding signalling is transmitted to thecorresponding subscriber, or that a virtual connection is forciblyinterrupted. Furthermore, an appropriate counter-measure can also becomprised in initially only marking the corresponding packets and thendiscarding them when the load situation in the network in fact requiresthis. This counter-measure thus means that there can also be exceptionsin the above transgression rule that can be allowed when the loadsituation in the network allows it.

In addition to the peak bit rate, a mean bit rate (average over a longertime, for example over a time interval of a few minutes) can also serveas a criterion for the transmission capacity announced by a subscriberwhen transmitting data packets and to be observed during the existenceof the corresponding, virtual connection. The peak bit rate as well asthe mean bit rate together can also serve as a criterion. EuropeanPatent Application 90122430.3, incorporated herein by reference, isreferenced in this context.

As was already mentioned, the required peak bit rate as well as the meanbit rate are reported by a subscriber when setting up a virtualconnection. These rate values are defined by appropriate storage in theATM switching equipment reached first by the message stream of thissubscriber. Appropriate data are thus stored in this switching equipmentallocated to the corresponding, virtual connection. When sendingpacket-switched messages, the corresponding subscriber dare not exceedthis peak bit rate and this mean bit rate. For this purpose, thuscall-associated bit rate limit values are defined in the ATM switchingequipment by storing corresponding data (peak bit rate and/or mean bitrate).

As was already indicated, routes are sought, selected and defined incall-associated fashion with a route searching and selecting means whensetting up new virtual connections. The acceptability of the set up ofnew virtual connections with respect to each and every one of the ATMlinks respectively coming into consideration for such a set-up is thuschecked with reference to the bit rate limit values defined incall-associated fashion for the corresponding new virtual connections.This check is carried out taking the free bit rate transmissioncapacities respectively still available on the corresponding ATM linksinto consideration. ATM links initially fundamentally come intoconsideration or not for new virtual connections based on the structuretechnique of the corresponding switching matrix network. For a virtualconnection in the switching matrix network K that is intended to proceedvia the switching matrices v11 and v32, only the links z111 through z11mand z132 through zm32 come into consideration. The other links do notcome into consideration because--as is already seen in terms of theswitching matrix network structure--they are obviously not suitable forthe corresponding virtual connection. Of those links coming intoconsideration for setting up a new virtual connection, all aresubsequently checked to see whether the required transmission capacityis still present on each and every one of them. Let it then be assumedthat this transmission capacity is no longer present on the ATM linksz111 and z232 in the exemplary case under consideration. In this case,the new virtual connection cannot be set up via the ATM linksz111/z132/z112/z232. The desired virtual connection, however, can be setup via the ATM links z11m and zm32. To this extent, it can thus be seenthat a coincidence condition must be satisfied in view of thetransmission capacity that is still respectively available. Thiscoincidence condition is of critical significance for the routesearching. A check must thus be carried out to see whether thiscoincidence condition is respectively met.

The exemplary embodiment of an ATM switching equipment contains only athree-stage switching matrix network. The analogous case, however, isalso valid for four-stage switching matrix networks and multi-stageswitching matrix networks going beyond this.

Among the things shown in the drawing are an ATM link occupation memorythat is composed of the memory parts x1 through xk and y1 through yn.The free bit rate transmission capacities still respectively availableon the ATM links of the switching matrix network K are stored inlink-associated fashion with the assistance of this occupation memory.These stored capacities are utilized for the check already set forthearlier. Thus, the acceptability of the set-up of new virtualconnections with respect to each and every one of the ATM links cominginto consideration for them is checked with reference to the bit ratelimit values respectively defined for the corresponding, new virtualconnections, and with reference to the free bit rate transmissioncapacity that is still respectively available on the corresponding ATMlinks.

It is then provided that the virtual connections, which have anunlimited number of different possible bit rate limit values, arecombined in connection bit rate classes that are significantly fewer incomparison thereto and refer to dimensional ranges of the bit rate limitvalues. The virtual connections, of course, are initially requested bysubscribers with the assistance of selection information they output.The bit rate limit values they desire are thus subscriber-associated. Itfollows therefrom that the number of different, possible bit rate limitvalues is, of course, initially unlimited. Insofar as the respectiveterminal equipment technologically allows it, the subscribers can freelyselect the mean bit rate and the peak bit rate with which they intend totransmit.

When, given the request for a new virtual connection on the basis ofsubscriber signalling (dialing), the bit rate limit values freelyselected by the subscriber or defined by the respectively existingterminal equipment arrive, then these are first allocated to dimensionalranges of the bit rate limit values. This applies both to the mean bitrate as well as to the peak bit rate. The relationship between mean bitrate and peak bit rate is thus also not defined. Connection requests canbe specified wherein the corresponding subscriber would like to transmitin extremely steady fashion. In this case, the peak bit rate hespecifies is no higher than or only slightly higher than the mean bitrate he specifies. In another instance, there can also be call requestswherein a subscriber only intends to transmit in extremely sporadicfashion during the existence of a virtual connection he has requested.In this case, he specifies what is only a relatively low, mean bit rate,by contrast whereto the peak bit rate that he has made use of can bequite, significantly higher. The bit rate limit values specified by thesubscribers are thus then allocated to defined dimensional ranges of thebit rate values. These dimensional ranges relate both to the limitvalues of the mean bit rate as well as to the limit values of the peakbit rate.

Connection bit rate classes are now formed which are identified bydifferent dimensional ranges of the bit rate limit values. A connectionbit rate class is characterized by a dimensional range with respect tothe mean bit rate and by a different dimensional range with respect tothe peak bit rate. The different connection bit rate classes can also bein part characterized by identical dimensional ranges with respect tothe mean bit rate and by different dimensional ranges in view of thepeak bit rate and vice versa.

Preferably, the connection bit rate classes that differ from one anotheron the basis of the dimensional ranges of the bit rate limit values inthe manner set forth above are numbered. On the basis of the numberingof a connection bit rate class, thus the respective dimensional range ofthe bit rate limit value with respect to the mean bit rate, as well asthe dimensional range of the bit rate limit value in view of the peakbit rate, are thus defined.

When a subscriber at subscriber station T wishes to set up a virtualconnection, then in addition to the standard selection information, healso--among other things--outputs the bit rate limit values with respectto the mean bit rate and with respect to the peak bit rate to thecorresponding switching center. These limit values, for example, can beaccepted in a subscriber line circuit R and can be forwarded from thelatter to a central processor P that controls the set-up of the virtualconnections in call-associated fashion and, among other things, acceptsthese two bit rate limit values and initially stores them for eachdesired, virtual connection.

In the same way, the free transmission capacities that are stillrespectively available on the ATM links are combined in transmission bitrate classes having corresponding transmission bit rate limit values.The ATM links, of course, respectively have a defined, maximumtransmission capacity. Some of the transmission capacity of thecorresponding ATM link is already being made use of by virtualconnections already set up via an ATM link. When setting up a newvirtual connection, only the remaining, free transmission capacity canthen be made use of. Only this is thus available for virtual connectionsto be newly set up. This is quite generally valid, i.e. under the aspectof taking peak bit rates and/or mean bit rates into consideration. TheATM link occupation memory that shall be referred to below as a"route-searching memory" for purposes of simplification, serves thepurpose of acquiring the transmission capacities free per ATM link intransmission bit rate classes having corresponding transmission bit ratelimit values. This route-searching memory is composed of the memoryparts x1 through xk and y1 through yn. The ATM links in the switchingmatrix network K form ATM link groups. An ATM link group always departsfrom a switching element, or leads to such a switching element. Forexample, such an ATM link group is composed of the ATM links z111through z11m. It departs from the switching element v11. Another ATMlink group, for example, is formed of the ATM links z132 through zm32.It leads to the ATM switching element v32. The analogous case applies toall other ATM links in the switching matrix network K.

At the output side, ATM trunks or corresponding subscriber lines areconnected to the switching elements v31 through v3n in a known way.These lead to other ATM switching centers. Only two such ATM trunks g1and g2 ar shown.

A family of storage cell lines, for example x11 through x18, is thenprovided in the route-searching memory per ATM link group, for examplez111 through z11m. One respective storage cell line, for example x11, isallocated to one of the transmission bit rate classes. The size of thisfamily is thus not dependent on the number of ATM links in an ATM linkgroup, but is based on the number of transmission bit rate classes thatare provided overall.

As may be seen from the drawing, the storage cell lines x11 through xk8and y11 through yn8 are subdivided into columns 111 through 11m and 131through m31. One respective storage cell (storage location) is acomponent part of a storage cell or row and simultaneously alsorespectively belongs to a defined column, for example 111.

Within each and every storage cell row, for example x11, the individualstorage cells (one respective storage cell per column) are individuallyallocated to the links, for example z111 through z11m, connected to therespective ATM switching element, for example v11. These storage cellscan be binarily signified, i.e. they can assume the logical value ofzero and the logical value of one. As a result, they indicate theavailability of transmission capacities with respect to the respectivetransmission bit rate class present on these ATM links. Let this besignified in that the respective storage cell carries the logical valueof one. As a result thereof, it indicates for the allocated ATM link,for example z111, to which, of course for example the column 111 isallocated, that transmission capacity is still available on this ATMlink for the respective transmission bit rate class.

As already stated, a respective storage cell row corresponds to atransmission bit rate class. As was likewise already explained above,this bit rate class can be characterized by two bit rate limit values(of the above dimensional ranges) wherein one relates to the mean bitrate and one relates to the peak bit rate. As a result of so signifying,it is thus indicated for a defined ATM link (a column correspondsthereto) whether transmission capacity is still available at this ATMlink in view of the respective transmission bit rate class that isidentified by defined dimensional ranges of the bit rate limit values.Thus, these bit rate limit values (as already indicated) refer, on theone hand, to the mean bit rate and, on the other hand, to the peak bitrate.

When, via his subscriber station T, a subscriber then places the orderto set up a new virtual connection, then, in addition to containing thedestination information (for example, subscriber telephone number), thisalso contains particulars about the desired, mean bit rate and about thepeak bit rate. On the basis of these particulars, the desired virtualconnection is allocated to the corresponding dimensional ranges based onthe measure of the bit rate limit values (relating to the mean bit rateand peak bit rate); the desired connection is thus assigned to a definedconnection bit rate class. For this purpose, these particulars areforwarded from the subscriber line circuit R to a processor P that,among other things, undertakes these allocations. This processor alsoreceives the destination information (dial information) on the basiswhereof it initiates the set-up of the desired virtual connection acrossan interface means E in the ATM switching matrix network. This occurs ina known way. During the route search itself, however, the processorproceeds in the manner of the invention.

Let it now be assumed that the destination information (for example,long-distance digit plus local area code plus subscriber telephonenumber) leads to a virtual connection being set up via the switchingelement v32. Let it be assumed that the dialing subscriber is thesubscriber at the subscriber station T. The desired virtual connectionis thus to be set up, among other things, across the switching elementv11 (see connection between R and v11 in the drawing FIGURE). Thequestion is now to seek a suitable route across the switching matrixnetwork. The link groups z111 through z11m and z132 through zm32 comeinto consideration for this. The processor forwards an informationconcerning this to the route-seeking means L that has the job ofseeking, selecting, and defining a suitable, free route. Up to thispoint, it is now already certain on the basis of the information thatthe route-seeking means L has received, that a corresponding free routeis to be sought in the link group z111 through z11m on the one hand andz132 through zm32 on the other hand. These two link groups correspond tothe two memory parts x1 and y2.

With the assistance of its read means Lx and Ly, the route-seeking meansL drives the memory parts x1 and y2. The processor also informs the readmeans L of the bit rate class that is the determining factor for thedesired virtual connection. On the basis of the information about thebit rate class and with the assistance of its read means Lx and Lywithin the memory parts x1 and y2, the route-seeking means L now selectsthose storage cell rows within these memory parts which are assigned tothe bit rate class. Among those ATM links that are coincidentallysignified by a logical one in view of the succession of the columns 111through 11m and 131 through m31, the route-seeking means L now seeks afree ATM link within the two storage cell rows. Of course, these twological values can also be interchanged.

In the corresponding two storage rows, the two read means Lx and Ly thusprogressively read the contents of the individual storage cellscolumn-by-column progressing from left to right, namely storage cell bystorage cell simultaneously in each of the two storage cell rows. Such asearch sequence is referred to as one having a fixed zero position.However, a search sequence that has a progressive zero position or azero position that changes randomly or in some other way can also beutilized. As soon as the route-seeking means L simultaneously receives arespective logical one via each of its two read means Lx and Ly, it canrecognize that the transmission capacity for the desired bit rate classis still free at the corresponding two ATM links, and a new virtualconnection is thus available for the equipment.

As stated, the corresponding bit rate class guarantees that a mean bitrate and a peak bit rate which correspond to the dimensional ranges ofthe bit rate limit values can be communicated via the correspondingvirtual connection. With reference to the bit rate limit value or to thebit rate limit values (expressed by the corresponding bit rate class)applying to the virtual connection to be respectively newly set up, astorage cell is sought whose allocated transmission bit rate classcorresponds to these two bit rate limit values, and thus to the desiredbit rate class in view of the transmission capacity required for the newvirtual connection.

One of those links whose storage cells are signified is selected withinthe corresponding storage cell row. This occurs in accordance with anafore-mentioned selection mode provided for the route seeking. This canprovide that a selection having a fixed zero point and a constant searchsequence is applied. However, other selection modes can also be applied,for example having a non-fixed zero position and/or having a non-fixedsearch sequence.

In the above-described way, a selection of ATM links in accordance withthe storage cell rows coming into question occurs according to theinvention in the various ATM link groups of non-identical switchingmatrix stages. This is done in dependence upon a coincidence in view oftheir signification existing within these storage cell rows for storagecells that correspond to one another. Storage cells corresponding to oneanother are thus storage cells that lie in columns having the same name,for example 112 and 231.

The description provided herein refers to switching matrix networkshaving in-line grouping. The corresponding case applies by analogy givenemployment of the invention in a switching matrix network havingswitching equipment comprising wraparound grouping.

It has already been pointed out that the switching matrix network canalso be constructed with more than three switching matrix stages. Theroute search is then also to be correspondingly designed, whereby acoincidence formation is to be provided in the inventive way not onlybetween two signified storage cells, but between correspondingly morestorage cells. Instead of being defined according to the criterion oftwo limit values (mean bit rate and peak bit rate), the connection bitrate classes as well as the transmission bit rate classes can also bedefined based on the criterion of one or more limit values.

In the present instance, eight different storage cell rows are providedper memory part (for example x1, y1). These correspond to eightconnection bit rate classes and eight transmission bit rate classes.These can be characterized by two different dimensional ranges in viewof the peak bit rates, and by four different dimensional ranges in viewof the mean bit rates.

Among other things, the functioning of the processor also covers thewrite-in of the significations into the individual storage cells of thestorage cell rows for each of the ATM links. Proceeding from the actualload condition on an ATM link, the transmission capacity that is stillrespectively free and available for new virtual connections isidentified for this purpose. The storage cell for the respective ATMlink is then signified in those storage cell rows that correspond totransmission bit rate classes having the identified transmissioncapacity as well as lower transmission capacity, and that are allocatedto transmission bit rate limit values corresponding thereto. When, forexample, the transmission capacity that is still free on the ATM linkz112 is identified, then the write means P1--in conjunctiontherewith--is first set to the memory part (x1) to which the ATM linkz112 is allocated. When the transmission capacity that is still free,i.e. that is still available for new virtual connections with respect tothe ATM link z112 has been identified, then the write means P1 enterslogical zeros in part, and logical ones, in part, into the column 112corresponding to this ATM link z112. Logical ones are thus written intothe storage cells of all of those storage cell rows for which adequatetransmission capacity is still present and available on the ATM linkz112. This shall be set forth in somewhat greater detail later.

In a further memory area for every ATM link and with respect to allconnections established thereover, the processor forms and stores,first, the sum of the mean bit rates of these connections, and second, aproduct sum wherein the individual products are respectively formed fromthe mean bit rate and the difference between the peak bit rate and themean bit rate of one of the virtual connections, i.e. the products areformed in call-associated fashion. For example, this special memory areacan be a component part of a column, for example 112, in a memory part,for example x1. This special memory area will thus be allocated to theATM link z112.

The processor P forms the sum as well as the product sum anew whensetting up a new virtual connection as well as when clearing down avirtual connection that had been set up. This can occur in such fashionthat the mean bit rate of the virtual connection that respectivelychanges the occupation situation, and the product corresponding to thisvirtual connection, are employed for incrementing or for decreasing thesum as well as the product sum, i.e. bringing them to the respectivecurrent status.

As was already stated, the central processor determines whether at leastone new virtual connection of the connection bit rate classcorresponding to the respective transmission bit rate class can be setup. This is determined for each ATM link based upon the mean bit ratesand the peak bit rates of the virtual connections already set up viathis link and proceeding from the mean bit rate and peak bit rate ofeach and every one of the transmission bit rate classes. In terms oftime, these calculating operations are implemented by the processorfollowing the route-searching procedures. The route-searching proceduresare thus far less critical in terms of their chronological urgency, andare also simplified, since they are reduced to simple one-bit comparisonevents. In particular, however, this also has an extremely positiveinfluence with respect thereto, since the calculating events can belimited to those ATM links which are now directly affected by the set-upor clear-down of a virtual connection.

For every ATM link where something with respect to the occupationsituation has changed (i.e. not only when setting up a new virtualconnection but in the analogously corresponding fashion at everyclear-down thereof as well), the processor thus successively calculatesthe possibilities for virtual connections in the various bit rateclasses. This is based on the mean bit rate and on the peak bit rate ofeach of the virtual connections already set up via this ATM link. Thesum and product sum that are already formed are preferably used for thispurpose. Proceeding on the basis of the mean bit rate and peak rate ofeach and every one of the possible transmission bit rate classes, theprocessor calculates whether at least one new respective virtualconnection of the bit rate class corresponding to the respectivetransmission bit rate class can still be set up in view of thetransmission capacity that is still available. Both the product sum aswell as the sum of the mean bit rates for the virtual connections thatare already set up are utilized for this purpose, and the correspondingproduct and the corresponding mean bit rate for a virtual connection ofone of the various bit rate classes are also added to the product sumand to the sum of the mean bit rates. The processor thus forms a productsum as well as a sum of the mean bit rates for the virtual connectionsthat are already set up as well as for a virtual connection of one ofthe various bit rate classes. The processor sequences this per bit rateclass. From the product sum acquired in this way, it then forms a squareroot value and multiplies the latter by an enlargement factor. It thenadds the sum of the mean bit rates thereto and thus forms a comparisonvalue which is the result of this addition. When this comparison valuethen does not exceed the maximum transmission bit rate of the ATM linkcoming into consideration, this ATM link is signified in the storage rowcorresponding to the respective transmission bit rate class, i.e. alogical one is written in. Otherwise, a logical zero is written in.

Let the comparator V also be pointed out. This serves for theimplementation of the coincidence check that has already been set forth.A determination that links corresponding to one another arecoincidentally signified is thus made with the assistance of thiscomparator V.

European Patent Application 90122430.3 has already been referenced.Among the things disclosed therein is that the comparison event setforth can also be modified. This, of course, is also true givenapplication of the contents of this earlier application to the case ofthe present invention. Thus, it is also possible that the processormakes the comparison value even somewhat more precise. It is accordinglyprovided that it selects the highest peak bit rate from the peak bitrates of the virtual connections already set up via the respective ATMlink, and also adds the amount thereof to the comparison value and onlythen implements the described comparison.

An enlargement factor was mentioned above and this shall be set forth insomewhat greater detail below. There is a high degree of probabilitythat the case will not occur that bit rates that are so extensive thatthe transmission capacity of an ATM line is exceeded occur on an ATMline during practical operation. Let it be assumed that a probability of10⁻⁹ is demanded. The size of the enlargement factor essentially resultsfrom this exponent (-9). Given a probability of 10⁻⁹ through 10⁻¹⁰ (withwhich thus a loss of cells occurs), this amounts to approximately 8 to9. The boundary conditions are that a) an ATM line is operated with agross transmission capacity of approximately 150 Mbit/s ("gross" meansincluding header of the ATM cells), b) the peak bit rates of the virtualconnections that are conducted via this ATM line do not exceed 2 Mbit/s,and c) the ratio of mean bit rate to peak bit rate in each of theconnections lies between 0.1 and 0.9.

In conclusion, let it also be pointed out that the above-describedswitching equipment can also be modified in the following way. First, aplurality of ATM link occupation memories corresponding in number to theplurality of ATM link groups can be provided, instead of one ATM linkoccupation memory (route-searching memory) for the ATM link groups, thisplurality of ATM link occupation memories being drivable in parallel inthe above-described route search. Second, the above-described functionsof the route-searching means L can also be executed by the processor P.

Although various minor changes and modifications might be proposed bythose skilled in the art, it will be understood that we wish to includewithin the claims of the patent warranted hereon all such changes andmodifications as reasonably come within our contribution to the art.

We claim as our invention:
 1. A method for setting up virtualconnections in ATM switching equipment operating according to anasynchronous transfer mode, comprising the steps of:providing amulti-stage ATM switching matrix network having a plurality of switchingmatrix stages each having a plurality of ATM switching elements, andwherein ATM links lead from switching matrix stage to switching matrixstage, and with the ATM switching elements connecting successiveswitching matrix stages to one another; defining and storing bit ratelimit values in call-associated fashion for individual virtualconnections; providing an ATM link occupation memory for set-up of newvirtual connections by selecting associated routes, free bit ratetransmission capacities which are still available being individuallystored therein for the ATM links; checking acceptability of the set-upof new virtual connections with respect to each and every one of the ATMlinks coming into consideration for these connections by use of the bitrate limit values defined for the new virtual connections and by use ofthe free bit rate transmission capacity that is still respectivelyavailable on the corresponding ATM links; allocating the virtualconnections to connection bit rate classes referring to dimensionalranges of the bit rate limit values, and allocating the free bit ratetransmission capacities still respectively available on the ATM links totransmission bit rate classes having corresponding transmission bit ratelimit values; combining into an ATM link group ATM links respectivelyexiting from one of the ATM switching elements and/or leading to such anATM switching element; reserving in the ATM link occupation memory meansto each of the ATM link groups a family of storage cells each having arespective plurality of storage locations, each of the storage cellsbeing allocated to a defined connection or transmission bit rate class,and within the respective storage cell each of the storage locationsbeing allocated to one of the ATM links connected to the respective ATMswitching element; marking in binary fashion the individual storagelocations of a storage cell given a presence of a free transmissioncapacity on the allocated ATM link for the transmission bit rate classallocated to the respective storage cell; for setting up a new virtualconnection via a plurality of ATM links corresponding in number to theplurality of switching matrix stages, selecting for every one of the ATMlink groups coming into consideration a storage cell corresponding tothe connection bit rate class allocated to the new virtual connection;interrogating the individual storage locations identically defined withrespect to the sequence within the storage cells just being driven; andbased on the interrogating, selecting for the new virtual connectionthose ATM links whose allocated storage locations have a coincidencywith respect to their binary identification.
 2. A method according toclaim 1 wherein said bit rate limit values for the individual, virtualconnections comprise mean bit rate values.
 3. A method according toclaim 2 wherein connection bit rate classes or transmission bit rateclasses are formed that differ from one another on the basis ofdifferent mean bit rates.
 4. A method according to claim 1 wherein saidbit rate limit values for the individual, virtual connections comprisepeak bit rate values.
 5. A method according to claim 4 whereinconnection bit rate classes or transmission bit rate classes are formedthat differ from one another on the basis of different peak bit rates.6. A method for setting up virtual connections in ATM switchingequipment operating according to an asynchronous transfer mode,comprising the steps of:providing a multi-stage ATM switching matrixnetwork having a plurality of switching matrix stages each having aplurality of ATM switching elements, and wherein ATM links lead fromswitching matrix stage to switching matrix stage, and with the ATMswitching elements connecting successive switching matrix stages to oneanother; defining and storing bit rate limit values in call-associatedfashion for individual virtual connections; providing an ATM linkoccupation memory for set-up of new virtual connections by selectingassociated routes, free bit rate transmission capacities which are stillavailable being individually stored therein for the ATM links; checkingacceptability of the set-up of new virtual connections with respect toeach and every one of the ATM links coming into consideration for theseconnections by use of the bit rate limit values defined for the newvirtual connections and by use of the free bit rate transmissioncapacity that is still respectively available on the corresponding ATMlinks; allocating the virtual connections to connection bit rate classesreferring to dimensional ranges of the bit rate limit values, andallocating the free bit rate transmission capacities still respectivelyavailable on the ATM links to transmission bit rate classes havingcorresponding transmission bit rate limit values; combining into an ATMlink group ATM links respectively exiting from one of the ATM switchingelements and/or leading to such an ATM switching element; reserving inthe ATM link occupation memory means for each of the ATM link groups afamily of storage cells each having a respective plurality of storagelocations, each of the storage cells being allocated to a definedconnection or transmission bit rate class, and within the respectivestorage cell each of the storage locations being allocated to one of theATM links connected to the respective ATM switching element; marking inbinary fashion the individual storage locations of a storage cell givena presence of a free transmission capacity on the allocated ATM link forthe transmission bit rate class allocated to the respective storagecell; setting up a new virtual connection via a plurality of ATM linkscorresponding in number to the plurality of switching matrix stages byselecting for every one of the ATM link groups coming into considerationa storage cell corresponding to the connection bit rate class allocatedto the new virtual connection; interrogating the individual storagelocations identically defined with respect to the sequence within thestorage cells just being driven; based on the interrogating, selectingfor the new virtual connection those ATM links whose allocated storagelocations have a coincidency with respect to their binaryidentification; proceeding from a momentary actual load condition and atevery set-up of a virtual connection or clear-down of an existingvirtual connection on the ATM links coming into consideration, updatingthe free transmission capacity that is still respectively available fornew virtual connections for the individual transmission bit rate classesby forming a transmission bit rate value for each of the ATM links basedon at lease one of mean bit rates or peak bit rates of all virtualconnections already set up via the respective ATM link and based on atleast one of a mean bit rate or peak bit rate corresponding to therespective transmission bit rate class; and when the calculatedtransmission bit rate value is lower than or equal to a maximumtransmission bit rate defined for the respective ATM link, identifyingin binary fashion the storage location corresponding to the respectiveATM link in the storage cells allocated to the respective transmissionbit rate class and to the transmission bit rate classes that are lowerin comparison thereto.
 7. A method according to claim 6 including thesteps of:for calculating the transmission bit rate value for therespective ATM link and at every set-up or clear-down of a virtualconnection, updating a sum of the mean bit rates of all virtualconnections set up thereover, and updating a product sum, and formingindividual products deriving from the mean bit rate and a differencebetween the peak bit rate and the mean bit rate of one of the set-up,virtual connections; expanding a corresponding sum or product sum by themean bit rate or by a product of a virtual connection corresponding tothe transmission bit rate classes, said product corresponding to theproducts contained in the product sum; and adding a square root value ofthe expanded product sum multiplied by a magnification factor to theexpanded sum of the mean bit rates.